Hello Luciana
When opening the file this afternoon the lost scene was back again! Yeah!
So, I immediately moved the file to the local harddrive. Yet, I want to make regular backups to the cloud drive. Another tool I am working with, Techsmith's Camtasia, has a built-in option to save a complete project as a .zip file with just one click. I don't see such a function in Storyline but would like to suggest integrating such a function. Of course, I can zip the project manually, but doing it right out of Storyline would be very convinient.
I am also happy if you have any further suggestions about secure file handling.